Using telnet command to check for open ports

[Product_Support]

Issue

Need to verify whether specific network ports are open, as certain ports may be blocked.

Product Line

Andover Continuum, EcoStruxure Building Expert, EcoStruxure Building Operation, Field Devices, Pelco, Satchwell MicroNet, Satchwell Sigma, TAC IA Series, TAC INET, TAC Vista

Environment

• TCP/IP Communication
• Command Prompt
• Telnet Command

Cause

Suspected network port blockage affecting communication between devices or applications.

Resolution

You can check if a port is open using the Telnet command in Command Prompt.

⚠️ Note: Telnet uses the TCP protocol only. It cannot be used to test UDP connectivity.

📌 Command Syntax:

telnet [domainname or IP] [port]

• [domainname or IP] – The server's domain name or IP address.
• [port] – The port number the server application is listening on.

🧪 Examples:

• telnet 192.168.0.20 9001 → Closed port: Displays a "connect failed" message.

   

• telnet 192.168.0.20 9003 → Open port: Displays a blank screen.

  

🚪 To Exit Telnet Session:

1. Press Ctrl + ]
2. Type quit and press Enter.

📝 Note: Telnet may be disabled by default on some machines. Refer to Microsoft's documentation for instructions on enabling Telnet.